(as of August 31, 2022)
The NASA EOS Aura mission, launched July 15, 2004, measures the composition of Earth’s atmosphere and solar spectral irradiance (SSI), providing essential data for understanding how Earth’s radiation balance, air quality, and ozone layer respond to changes atmospheric composition caused by both human activities and natural phenomena. Thus, the Aura mission directly addresses the first Earth Science research objective in the NASA 2014 Science Plan — “Advance the understanding of changes in the Earth’s radiation balance, air quality, and the ozone layer that result from changes in atmospheric composition”. Aura’s two remaining instruments, the Microwave Limb Sounder (MLS) and the Ozone Monitoring Instrument (OMI), have been the cornerstones of the Aura Mission since launch, providing unique measurements and stable, long-term climate records.
Insufficient power generation (by the solar array) is predicted to be the life-limiting factor for the Aura Mission. The intersection of the two lines represents the latest date (August 2025) when Aura will have sufficient power for continued operations. The increase in the number of “strings” on the solar array required in 2025 is driven by an increase in the solar beta angle, which determines the amount of power generated. The cause of the increase in the beta angle is discussed in the following slides.
Since launch in 2004, the polar sun synchronous orbit of the spacecraft has been stable and repeatable through periodic spacecraft maneuvers (i.e., inclination adjust, IAM, and drag make-up, DMU, maneuvers), which require fuel to maintain Aura’s position in the A-Train constellation of satellites. The final IAMs were done in spring of 2022 to save remaining fuel. Consequently, the spacecraft will slowly begin to drift over time (next slide). Aura will have sufficient fuel remaining for a possible exit from the A-Train Constellation in August 2024 and to continue performing DMUs to maintain altitude and risk mitigation maneuvers (RMMs) for mission safety.
An indicator of the drift is the mean local time (MLT) crossing of the spacecraft over the equator during the day. The graph shows the possible temporal evolution of this drift, which is <15 min through mid-2024 and ~50 min by the end of the mission. Overall, this amount of drift is predicted to be minor from the perspective of data quality for all MLS data products and almost all of OMI ones. That is, the MLS and OMI instrument teams will be able to account for this minor drift in the data product retrieval algorithms.
On about August 6, 2024, the Aura satellite has the possibility to exit the A-Train constellation, descending in altitude through a series of maneuvers. If these maneuvers are performed, Aura’s orbit since launch will no longer be maintained and the MLT drift will increase. The graph below shows that the altitude of the highest altitude of the orbit (apogee) and the lowest altitude (perigee) will diverge and begin to oscillate. The retrieval algorithms of both the MLS and OMI data products will be able to account for these changes in altitude, ensuring high fidelity of the data products. One exception is for the OMI solar spectral irradiance data product, whose trend quality will degrade after late 2024 when the science upper limit of the beta angle is exceeded (next slide).
As mentioned in the previous slide, the MLS and OMI retrieval algorithms can account for potential changes in the solar beta angle so that data product quality will be unaffected. One exception is for the OMI solar spectral irradiance (SSI) data product, which is sensitive to changes in the beta angle. A potential beta angle violation of the “science upper limit” in late 2024 will increase uncertainties in the OMI SSI data product thereafter.
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